Colloidal semiconductor quantum dots (CQDs) have been considered as a promising material platform for the realization of solution-processed lasers. In addition to wide range spectral tunability thanks to quantum confinement, CQDs offer other interesting properties for lasing applications including atomic-like discrete energy levels and chemical stability, making them compatible with any arbitrary substrate and optical cavities . However, CQD-lasers have suffered severely from poor gain performances, making them impractical for feasible daily-life applications. The fundamental limitations of the CQDs as a gain medium arise from non-unity degeneracy of the band-edge state . Then, to achieve light amplification, at least some of the CQDs must contain more than one exciton. An additional complication is associated with nonradiative Auger recombination, whereby the electron–hole recombination energy is transferred to a third carrier. This results in Therefore, the low-threshold CQD-lasers at room temperature are essentially needed.
In the first part of the talk, I will discuss about the infrared lasers based on Pb-chalcogenide CQDs. Room-temperature tunable emission infrared lasers are achieved by integrating Pb CQDs to the distributed feedback cavity (DFB) . By engineering the Auger process in PbS CQDs at the supra-nanocrystalline level, we achieved low threshold highly stable single-mode infrared DFB-laser . Our recent result show that using heterostructured Pb-chalcogenide core/shell CQDs allows us to achieve sub-single-exciton laser for the first time in an infrared CQD materials . Additionally, I will talk about our dual functional device which operates as infrared light emitting diode and laser under electrical- and optical-excitation, respectively .
In the second part of my talk, I will present my research activities in realization of highly-efficient visible-emitting CQD-lasers. In doing so, we have designed and developed a heterostructure of CdSe-based CQDs, which led us to achieve record lowest gain/lasing threshold among all semiconductor nanocrystals . Additionally, we showed red-emitting multi-mode lasers which obtained by coupling these engineered CQDs heterostructure to a core-less optical fiber, in which lasing modes supported by whispering-gallery-mode resonator .
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Nima Taghipour is a PREBIST Marie Curie Ph.D. fellow at ICFO-Institute of Photonics Sciences, working in Functional Optoelectronics Nanomaterials under the supervision of professor Gerasimos Konstantatos. Prior to joining ICFO, Nima worked in UNAM-National Nanotechnology Center in the Quantum Devices and Sensors group as a postgraduate researcher at Bilkent University, Turkey. He received his B.Sc. in Electronics Engineering and his M.Sc. in Photonics Engineering in the same department at Tabriz university, Iran.
Nima's research is understanding excitonic properties of low-dimensional quantum confined materials including colloidal semiconductor quantum -dots, -wells and two-dimensional semiconductors. He uses these nanomaterials to develop novel light-detection and light-emitting devices especially lasers.
After being awarded the COFUND PREBIST Ph.D. fellowship under the Marie-Curie action on a proposal entitled “Optical Gain and Lasing in Infrared Colloidal Quantum Dots”, he joined ICFO to pursue his Ph.D. degree. His current research focuses on the lasing action of colloidal semiconductor quantum dot (CQDs) in the telecommunication band. The objective of his Ph.D. study is the demonstration of highly-performed infrared lasers based on CQDs.